“Over decoys” means various things to different people, I’ve learned. For this discussion, my response assumes 40 yards and less.
1) #3
2) Light or dark? Light- #1or #2; dark - #1 or BB; BBB if giants.
3) BBB or T. Much prefer heavier alternatives (Tungsten) and smaller sizes on cranes (all waterfowl actually, but especially cranes.)
I’m more of an F kind of guy with a turkey choke